A. Field of the Invention
This invention relates to a catalytic cracking process using a mesoporous aluminophosphate material modified with at least one element selected from zirconium, cerium, lanthanum, manganese, cobalt, zinc, and vanadium. Such materials have high surface area and excellent thermal and hydrothermal stability, with a relatively narrow pore size distribution in the mesoporous range.
B. Description of the Prior Art
Amorphous metallophosphates are known and have been prepared by various techniques. One such material is described in U.S. Pat. No. 4,767,733. This patent describes rare earth aluminum phosphate materials, which, after calcination, have a relatively broad pore size distribution with a large percentage of pores greater than 150 xc3x85. The typical pore size distribution is as follows:
U.S. Pat. Nos. 4,743,572 and 4,834,869 describe magnesia-alumina-aluminum phosphate support materials prepared using organic cations (e.g., tertiary or tetraalkylammonium or phosphonium cations) to control the pore size distribution. When organic cations are used in the synthesis, the resulting materials have a narrow pore size distribution in the range from 30 to 100 xc3x85. When they are not used, the pore size is predominantly greater than 200 xc3x85. U.S. Pat. No. 4,179,358 also describes magnesium-alumina-aluminum phosphate materials, materials described as having excellent thermal stability.
The use of aluminophosphates in cracking catalysts is known. For example, U.S. Pat. No. 4,919,787 describes the use of porous, rare earth oxide, alumina, and aluminum phosphate precipitates for catalytic cracking. This material was used as part of a cracking catalyst, where it acted as a metal passivating agent. The use of a magnesia-alumina-aluminum phosphate supported catalyst for cracking gasoline feedstock is described in U.S. Pat. No. 4,179,358. Additionally, a process for catalytic cracking high-metals-content-charge stocks using an alumina-aluminum phosphate-silica-zeolite catalyst is described in U.S. Pat. No. 4,158,621.
There remains a need in the art for highly stable aluminophosphate materials for use in catalytic cracking processes, as well as for simple, safe processes for producing these materials. The aluminophosphate materials preferably possess excellent hydrothermal and acid stability with uniform pore sizes in the mesoporous range, and provide increased gasoline yields with increased butylene selectivity in C4xe2x88x92 gas.
This invention resides in a process for catalytic cracking of a hydrocarbon feedstock comprising contacting the feedstock with a catalyst composition comprising a mesoporous aluminophosphate material which comprises a solid aluminophosphate composition modified with at least one element selected from zirconium, cerium, lanthanum, manganese, cobalt, zinc, and vanadium, wherein the mesoporous aluminophosphate material has a specific surface of at least 100 m2/g, an average pore diameter less than or equal to 100 xc3x85, and a pore size distribution such that at least 50% of the pores have a pore diameter less than 100 xc3x85.
Preferably, the mesoporous aluminophosphate material has an average pore diameter of 30 to 100 xc3x85.
Preferably, the catalyst composition also comprises a primary catalytically active cracking component.
Preferably, the primary catalytically active cracking component comprises a large pore molecular sieve having a pore size greater than about 7 Angstrom.